As the problems relating to the design and fabrication of broadband optical fibers are being successfully resolved, attention is now shifting to the investigation of methods for exploiting their great potential. Among the items being investigated are wavelength selective filters for separating a plurality of signals propagating along a common wavepath. Typically, directional couplers are employed for this purpose, as described, for example, in U.S. Pat. No. 4,243,295. Because such devices rely upon the interaction of evanescent fields they tend to be longer than one might prefer. In addition, they require the fabrication of two, closely spaced lightguides and associated electrodes and, as such, are relatively difficult structures to fabricate.